employing someone from EU

After a long standing vacant position( Physiotherapy)I have finally decided to employ someone from Spain(EU). I am a single person firm and have not done done this before.Does anyone here have an idea as to what the requirements to employ an EU citizen are necessary.?

forever besides the normal insurance, pension etc deduction I guess I will need to pay the Quellen Steuer too.?

thanks for any inputs

Sups